U.S. patent number 7,618,822 [Application Number 10/326,792] was granted by the patent office on 2009-11-17 for predictive crude oil compatibility model.
This patent grant is currently assigned to BP Corporation North America Inc.. Invention is credited to Michael R. Kimbrell, Sailendra Nemana, Eugene Zaluzec.
United States Patent |
7,618,822 |
Nemana , et al. |
November 17, 2009 |
Predictive crude oil compatibility model
Abstract
A method for blending at least two hydrocarbon liquids, the
method comprising: (a) determining the critical solvent power for
each hydrocarbon liquid by (i) mixing each hydrocarbon liquid with
predetermined amounts of a paraffin; (ii) centrifuging each
resulting mixture; (iii) recovering and weighing any resulting
precipitated insolubles from step (ii); and (iv) correlating the
weight of the insolubles in step (iii) to the solvent power at
which asphaltenes begin to precipitate out of the hydrocarbon; (b)
determining the solvent power for each hydrocarbon liquid by: (i)
determining the distillation curve and density of each hydrocarbon
liquid; (ii) numerically integrating the distillation curve of each
hydrocarbon liquid, producing the volume average boiling point for
each hydrocarbon liquid; (iii) calculating the characterization K
factor for each hydrocarbon liquid using the volume average boiling
point in step (ii); and (iv) determining the solvent power of each
hydrocarbon liquid using the characterization K factor in step
(iii), wherein heptane and toluene are used as solvent power
references wherein heptane has a solvent power of zero and toluene
has a solvent power of 100; and (c) blending the each crude oil
into each other producing a crude oil blend wherein the solvent
power of the crude oil blend is greater than the critical solvent
power of the crude oil having the highest critical solvent power in
the blend.
Inventors: |
Nemana; Sailendra (Carmichael,
CA), Kimbrell; Michael R. (Huntington Beach, CA),
Zaluzec; Eugene (Garden Grove, CA) |
Assignee: |
BP Corporation North America
Inc. (Warrenville, IL)
|
Family
ID: |
32594116 |
Appl.
No.: |
10/326,792 |
Filed: |
December 19, 2002 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20040121472 A1 |
Jun 24, 2004 |
|
Current U.S.
Class: |
436/29; 436/139;
436/179; 436/25 |
Current CPC
Class: |
C10G
75/00 (20130101); G01N 33/2823 (20130101); Y10T
436/12 (20150115); Y10T 436/21 (20150115); Y10T
436/25625 (20150115) |
Current International
Class: |
G01N
33/24 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Lin "The relationship between the characterization factor "K" and
the solubility parameter ".delta." of petroleum solvents",
Proceedings of the National Science Council, Republic of China
(1978), 2(3), 314-21. cited by examiner .
The Oil Compatability Model And Crude Oil Incompatability, Erwin A.
Wiehe, Corporate Research Laboratories, Exxon Research and
Engineering Company. cited by other .
Mitigation of the Plugging of a Hydrotreater with the Oil
Compatibility Model, Erwin A. Wiehe, Corporate Research
Laboratories, Exxon Research and Engineering Company. cited by
other .
Prevention of Fouling by Incompatible Crudes with the Oil
Compatibility Model, Erwin A. Wiehe, Corporate Research
Laboratories, Exxon Research and Engineering Company. cited by
other.
|
Primary Examiner: Gakh; Yelena G
Attorney, Agent or Firm: Schoettle; Ekkehard
Claims
That which is claimed is:
1. A crude oil blend comprising two or more crude oils blended by a
method comprising the steps of: (a) determining the critical
solvent power for each crude oil by: (i) mixing each crude oil with
predetermined amounts of a paraffinic hydrocarbon having a solvent
power of zero; (ii) centrifuging each resulting mixture; (iii)
recovering and weighing any resulting precipitated asphaltenes from
step (ii); and (iv) correlating the weight of the precipitated
asphaltenes in step (iii) to the solvent power at which asphaltenes
begin to precipitate out of the crude oil; (b) determining the
solvent power for each crude oil by: (i) determining the
distillation curve and density of each crude oil; (ii) numerically
integrating the distillation curve of each crude oil producing the
volume average boiling point for each crude oil; (iii) calculating
the characterization K factor for each crude oil using the volume
average boiling point in step (ii); and (iv) determining the
solvent power of each crude oil using the characterization K factor
in step (iii); and (c) blending each crude oil into each other
producing a crude oil blend wherein the solvent power of the crude
oil blend is greater than the critical solvent power of the crude
oil having the highest critical solvent power in the blend; wherein
a Monte Carlo simulation is used to select a plurality of different
blend ratios of the two or more crude oils to calculate the solvent
power in step (b) of each crude oil blend.
2. The crude oil blend of claim 1, wherein the crude oil blend
comprises three or more crude oils.
3. The crude oil blend of claim 1, wherein the crude oil blend
comprises four or more crude oils.
4. The crude oil blend of claim 1, wherein the solvent power of the
crude oil blend is at least 5 percent greater than the critical
solvent power of the crude oil having the highest critical solvent
power in the crude oil blend.
5. The crude oil blend of claim 1, wherein the solvent power of the
crude oil blend is at least 10 percent greater than the critical
solvent power of the crude oil having the highest critical solvent
power in the crude oil blend.
6. The crude oil blend of claim 1, wherein the solvent power of the
crude oil blend is at least 15 percent greater than the critical
solvent power of the crude oil having the highest critical solvent
power in the crude oil blend.
Description
FIELD OF THE INVENTION
The present invention relates to a method for predicting the
compatibility or incompatibility of blending two or more
hydrocarbon liquids or crude oils together.
BACKGROUND OF THE INVENTION
In order to satisfy favorable economics for the refining of crude
oil, it is often necessary to blend two or more crude oils prior to
carrying out the various refining processes. However, there are
particular problems associated with blending crude oils. One major
problem is that crude oils are often incompatible with each other
resulting in equipment fouling and ultimately equipment shutdown.
Such equipment includes, but is not limited to, pipes, tanks, heat
exchangers, furnaces, fractionators and reactors. Another major
problem with blending crude oils and other hydrocarbons is the
production of oil and water emulsions in the crude oil slop system
preventing the oil slop from being processed by refinery equipment,
such as crude distillation units. Another major problem is the
production of emulsions in crude desalter units often having a
deleterious effect upon the waste water system associated with the
desalter unit. In light of these problems, crude oil
incompatibility has been plaguing the refining industry for many
years resulting in lost profits due to unnecessary equipment
shutdown and limitations on the crude oil slate available for
refining.
The primary culprit that causes incompatibility of crude oils is
the presence of organic solids in the form of precipitated
asphaltenes in blended crude oils. Current theory regarding the
asphaltene-crude oil relationship postulates that such relationship
is similar to a solute-solvent interaction wherein a certain
solvent strength is required to hold asphaltenes in solution in
crude oil. The primary parameter governing the ability of
asphaltenes to remain in solution in crude oil is the aromatics to
saturates ratio of the crude oil. It is known that asphaltenes are
soluble in aromatics such as toluene, but insoluble in paraffinic
compounds such as n-heptane. Accordingly, asphaltenes are defined
herein as the non-volatile and polar fraction of crude oil that is
insoluble in n-alkanes.
The underlying problem associated with the presence of asphaltenes
in crude oils is that asphaltenes frequently precipitate from
solution during the blending of two or more incompatible crude
oils. This is generally thought to be caused by perturbations of
the indigenous crude oil composition disrupting the delicate
balance that keeps the asphaltenes soluble in crude oil. It is also
believed that oil-water emulsions are formed and stabilized in part
by the presence of precipitated asphaltenes from incompatible crude
blends. Consequently, when left unchecked, asphaltene precipitation
manifests itself in a variety of undesirable areas, including
refinery equipment through the formation of coke and the generation
of oil-water emulsions in storage tanks.
In the past, crude oil compatibility could be determined through
extensive laboratory testing. For blends of two crude oils, the
determination of crude oil compatibility is relatively
straightforward since the number of tests required to define the
acceptable blend ratios is relatively small. However, for each
additional different stock of crude oil added to a blend, the
number of lab tests required to ascertain the range of
incompatibility goes up exponentially making the determination of
crude oil compatibility intractable. This presents a difficulty
when economic conditions justify blending three or more crude oils
together for feed to crude distillation units or other refining
processes. Accordingly, there is a need for a practical and cost
efficient means for determining the viability of blending different
crude oils.
In response to this need, the petroleum refining industry has
devoted extensive resources and effort to develop new methods to
solve the problem of blending different crude oils. However, such
efforts have only partially succeeded in providing a practical yet
cost effective method for blending different crude oils.
One such effort is U.S. Pat. No. 4,843,337 issued to Dickakian et
al., which discloses a method for blending hydrocarbon liquids at a
ratio to maintain the combined aromatic to asphaltene ratio above a
certain predetermined level to prevent fouling of process
equipment. However, the Dickakian disclosure is limited to a method
for blending two hydrocarbon liquids leaving unsettled the problem
of blending three or more crude oils.
U.S. Pat. No. 5,871,634 and U.S. Pat. No. 5,997,723, both issued to
Wiehe et al., disclose a method for blending potentially
incompatible crude oils by combining each crude oil in order of
solubility blending numbers such that the solubility blending
number of the mixture is greater than the insolubility number of
any crude oil of the mixture. However, the Wiehe disclosures
teaches a method that employs inexact and onerous laboratory tests,
such as conventional optical microscopy or crude oil filtration to
determine the presence of asphaltenes in each crude oil. Moreover,
the Wiehe disclosure employs a complex blending and titration
analysis to determine the insolubility number and the solubility
blending number for each crude oil.
Although the foregoing disclosures provide advances in the art,
there is still a need for a method for accurately determining crude
oil incompatibility that is practical and cost efficient.
It has also been found that centrifuging one or more crude oils
blended with predetermined amounts of heptane provides for a simple
yet cost effective means for determining asphaltene instability and
the amount of asphaltenes in each crude oil.
It has also been found that the relative ratio of aromatics to
saturates in each crude oil to be blended can be easily determined
by using the relationship between the boiling point and the density
of each crude oil.
It has also been found that compatible blends of two or more crude
oils can be determined based on the relationship between the
boiling point and the density of each crude oil in the blend and
the determination of asphaltene instability in each crude oil in
the blend.
SUMMARY OF THE INVENTION
The present invention is directed to a method for blending at least
two hydrocarbon liquids together by determining the critical
solvent power for each hydrocarbon liquid, determining the solvent
power for each hydrocarbon liquid, and thereafter blending the
hydrocarbon liquids together, producing a hydrocarbon liquid blend
having a solvent power that is greater than the critical solvent
power of the hydrocarbon liquid having the highest critical solvent
power in the blend.
As used herein, crude oil is understood to mean liquid petroleum
and all other hydrocarbons, regardless of gravity, produced at a
well in liquid form by ordinary production methods.
As used herein, a hydrocarbon liquid is understood to mean a fluid
compound comprising hydrogen and carbon.
As used herein, solvent power is understood to mean the relative
ratio of aromatics to saturates in a crude oil or a blend of crude
oils.
As used herein, critical solvent power is understood to mean the
solvent power at which asphaltenes begin to precipitate out of a
crude oil or blend of crude oils.
The present invention also includes a method for determining the
critical solvent power of one or more hydrocarbon liquids. The
method includes the steps of mixing each hydrocarbon liquid with
predetermined amounts of a normal paraffin, centrifuging each
resulting mixture recovering and weighing any resulting
precipitated insolubles from the mixture, and thereafter
correlating the weight of the insolubles to a solvent power at
which asphaltenes begin to precipitate out of the mixture.
The present invention also includes a method for determining the
solvent power of one or more hydrocarbon liquids. The method
includes the steps of determining the distillation curve and
density of each hydrocarbon, numerically integrating the
distillation curve of each hydrocarbon liquid, producing the volume
average boiling point for each hydrocarbon liquid, calculating the
modified characterization K factor for each hydrocarbon liquid
using the volume average boiling point, and thereafter determining
the solvent power of each hydrocarbon liquid using the calculated
modified characterization K factor wherein heptane and toluene are
used as solvent power references wherein heptane has a solvent
power of zero and toluene has a solvent power of 100.
The present invention provides for a practical yet cost effective
process for determining the solvent power of one or more
hydrocarbon liquids and/or crude oils that does not require the
complex blending and titration analysis to determine the
insolubility number and the solubility blending number for each
hydrocarbon liquids and/or crude oils.
The present invention also provides for a practical yet cost
effective process for determining the amount of asphaltenes in one
or more hydrocarbon liquids and/or crude oils allowing for the
determination of the optimal blend of two or more hydrocarbon
liquids and/or crude oils during a variety of economic
conditions.
The present invention also provides for a practical yet cost
effective process for determining the compatibility of two or more
crude oils together facilitating the flexibility of choosing a wide
variety of crude oil slates for processing in a crude oil
refinery
The present invention also provides a practical yet cost effective
process for blending two or more hydrocarbon liquids and/or crude
oils for processing in a refinery without the threat of asphaltene
precipitation reducing unit downtime due to fouling or coke
formation of lines or in equipment caused by incompatible blends of
crude oil.
The present invention also provides for energy savings by
preventing heat exchanger fouling caused by blending incompatible
hydrocarbon liquids and/or crude oils.
The present invention also provides for a method of eliminating
crude oil from desalter unit's effluent water preventing upsets in
the waste water system and wastewater discharge. Similarly, water
carry over with the oil from the desalter will be eliminated,
minimizing unstable operation of the crude distillation unit.
Although the subject invention is presented herein primarily as it
applies to crude oils, it is understood to one of ordinary skill in
the art that the subject invention may also be applicable with
other hydrocarbon liquids where precipitation of insolubles and
fouling are of concern.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 depicts an embodiment of a process in accordance with the
present invention graphically illustrating continuous predictive
modeling for blending three different crude oils together.
FIG. 2 depicts fouling level risks of a refinery process unit
resulting from the blending of multiple crude oils over a period of
time.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
In greater detail, the subject invention is directed to a method
for blending two or more crude oils together in a manner to prevent
asphaltene precipitation from the crude oil blend. More
particularly, the subject invention comprises a method for
determining the solvent power and critical solvent power of the
crude oils that are candidates for blending, and thereafter
blending the crude oils together such that the solvent power of the
blended crude oils is greater than the critical solvent power of
the crude oil having the greatest critical solvent power in the
blend. As previously stated, solvent power is understood to mean
the relative ratio of aromatics to saturates in a crude oil or a
blend of crude oils and critical solvent power is understood to
mean the solvent power at which asphaltenes begin to precipitate
out of a crude oil or a crude oil blend.
Each crude oil has a unique solvent power and unique critical
solvent power. If two or more crude oils are blended together, the
solvent power of the resulting blend varies between the solvent
powers of each crude oil in the blend. Considering this, it is of
paramount concern to accurately and precisely predict the solvent
power of a crude oil blend in order maintain asphaltenes in the
crude oil blend in a soluble state. To address this paramount
concern, the subject invention includes: (1) a method for
determining the solvent power of one or more crude oils; (2) a
method for determining the critical solvent power of one or more
crude oils, and (3) a method for blending two or more crude oils
together.
Determining Crude Oil Solvent Power
As previously stated, past practice used repetitive lab testing to
determine a crude oil's solvent power. Considering, however, that
the primary parameter governing the ability of asphaltenes to
remain in solution in crude oil is the aromatics to saturates ratio
of the crude oil, it is possible to accurately model crude oil as a
solvent using assay data, including distillation data and density
data, of the crude oil. By using the relationship between the
distillation data and the density data of a crude oil, the relative
ratio of aromatics to saturates in the crude oil can be determined.
Therefore, the solvent power of one or more crude oils can be
determined as more particularly described herein.
In determining the solvent power of a particular crude oil, it is
preferred to obtain assay data for the selected crude oil. The
preferred assay data are distillation data and density data of the
selected crude oil. If such data is not readily available or it is
suspected that available assay data is inaccurate, a conventional
high temperature simulated distillation can be easily conducted to
provide the preferred distillation data of a particular crude. The
density of the crude oil can be obtained by any conventional method
known to those skilled in the art.
Typical distillation simulations used in the refining industry are
ASTM and true boiling point (TBP) analytical distillations, which
are often both used to define the volatility characteristics of
petroleum fractions and other complex mixtures. Both are batch
distillations, which differ mainly in the degree of fractionation
obtained in the distillation. ASTM distillations are more
convenient than TBP distillations because ASTM distillations are
simpler, less expensive, require less sample, and require only
approximately one-tenth as much time. The ASTM distillations
methods used today include: ASTM Method D86; ASTM Method D1160;
ASTM Method D2887; ASTM Method D2892; and ASTM Method D3710. As is
appreciated by those skilled in the art, the method of distillation
employed often depends upon the petroleum fraction that is to be
distilled.
Although the distillation data from any of these distillation
methods is suitable for the subject invention, it is preferred that
the distillation data derive from an ASTM Method D86 distillation.
If the available distillation data for the present invention is not
from an ASTM Method D86 distillation, the distillation data is
preferably converted to a D86 distillation curve. This conversion
can be done manually according to the API method of conversion as
disclosed in API Technical Data Book, Chapter 3: Petroleum Fraction
Distillation Interconversions, 5.sup.th ed., 1992, which is
incorporated herein by reference. However, it is preferred to
conduct the conversion using HYSYS, PRO II, or any other computer
program that uses the API method of conversion. If HYSYS or PRO II
is used for the conversion, it is preferred that a probability
method of curve extrapolation is used.
The next step in determining the solvent power of a particular
crude is to numerically integrate the distillation curve,
preferably a D86 distillation curve, from 0% to 100% and divide by
100. This integration gives the volume average boiling point (VABP)
of the selected crude oil and is given by:
.intg..times..function..times.d ##EQU00001## In integrating the
distillation curve, the preferred method is to fit the distillation
curve to a cubic spline function (third order polynomial function),
which is then integrated numerically at 1% increments.
Once the distillation curve is integrated, it is preferred to
calculate the characterization factor K of the selected crude oil,
K.sub.oil, using the volume average boiling point and the density
of the selected crude oil. The characterization factor K is based
on Watson K factor as described in API Technical Data Book, Chapter
2: Petroleum Fraction Distillation Interconversions, 5.sup.th ed.,
1992, which is incorporated herein by reference. Preferably, the
calculation to determine the characterization factor K is given
by:
.times..times..times..times. ##EQU00002##
Once the characterization factor K of the selected crude oil is
calculated, the solvent power of the selected crude is easily
determined. The solvent power of the selected crude oil is
preferably defined using heptane and toluene as references, wherein
heptane has a solvent power of zero and toluene has a solvent power
of one hundred. Thus, a crude oil with solvent power of zero is
equivalent to heptane, and a crude oil with a solvent power of one
hundred is equivalent to toluene. Typically, most crude oils do not
have a solvent power greater than fifty, which is about cyclohexane
equivalent. Preferably, the determination of the solvent power of a
crude oil is given by:
.times. ##EQU00003## Thus: when SP=0, oil is approximately heptane
equivalent; when SP=100, oil is approximately toluene equivalent;
when SP=50, oil is approximately cyclohexane equivalent.
As one of ordinary skill in the art would appreciate, determining
the solvent power of one or more crude oils or hydrocarbon liquids,
as described herein, is relatively simplistic and provides a useful
tool in determining the compatibility of blending a plurality of
crude oils. Another useful yet simplistic tool in determining the
compatibility of blending a plurality of crude oils is the
determination of the critical solvent power of one or more crude
oils as described herein.
Determining the Critical Solvent Power
Experimental evidence shows that below a certain threshold solvent
power, asphaltenes precipitate out of crude oil. This threshold is
called the critical solvent power of the crude oil. At solvent
powers above the critical value, asphaltenes stay in solution and
precipitation is prevented. Considering that the solvent power of
crude oil is the relative ratio of saturates to aromatics, the
determination of the critical solvent power as contemplated herein
employs a simplistic paraffin (saturate) titration with each crude
oil that is a candidate for blending.
In accordance with the present invention, it is preferred that a
paraffin is incrementally added to a crude oil that is a candidate
for blending with one or more different crude oils. It is preferred
that the paraffin is normal heptane (n-heptane). However, other
paraffins, such as normal pentane or iso-octane, may be suitable
for the present invention. As the concentration of the paraffin
increases in the crude oil, the ratio of saturates to aromatics
increases until asphaltenes begin to precipitate out of the crude
oil. The point of initial asphaltene precipitation represents the
critical solvent power of the crude oil. The critical solvent power
of the tested crude oil is documented for future determinations of
its blending compatibility with other crude oils.
In a preferred embodiment, at least about a 50 ml. sample of the
selected crude oil is obtained to determine its critical solvent
power. Predetermined amounts of a suitable paraffin is
incrementally added to the crude oil sample, mixed and allowed to
equilibrate. It is preferred that n-heptane is incrementally added
to the crude oil sample in at least about 1:5 ratio as measured in
wt. %, vol. % or mol. %. It is more preferred that n-heptane is
added to the crude oil sample in at least about 1:10 ratio as
measured in wt. %, vol. % or mol. %. It is most preferred that
n-heptane is added to the crude oil sample in at least about 1:20
ratio as measured in wt. %, vol. % or mol. % for best results.
From the selected sample, it is preferred to prepare separate
solutions of the selected crude oil and n-heptane. The prepared
solutions preferably have varying ratios of n-heptane to the
selected crude oil. For example a 100 ml. sample of a selected
crude may be separated into 10 sample tubes. One sample tube
preferably contains 100 wt. % crude oil while the remaining nine
sample tubes preferably contain a solution of the selected crude
oil and varying amounts of n-heptane. The sample tubes preferably
have solutions with increasing concentrations of n-heptane,
preferably in 10% wt. % increments. For example, sample tube 1
contains 100 wt. % crude oil, sample tube 2 contains 90 wt. % crude
oil and 10 wt. % n-heptane, and sample tube 3 contains 80 wt. %
crude oil and 20 wt. % n-heptane, and so forth. A final sample tube
preferably has 100 wt. % n-heptane.
The samples are thoroughly mixed and allowed to equilibrate and
then centrifuged. The centrifuging process can be carried out by
any conventional centrifuge available on the market, such as an
Eppendorf Micro Centrifuge 5415C. The sample tubes are preferably
centrifuged at least about 10,000 rpm, more preferably at least
about 11,000 rpm, and most preferably at least about 12,000 rpm for
at least about 10 mins, more preferably at least about 15 mins and
most preferably at least about 20 mins.
After the samples have been centrifuged, the supernatant liquid is
removed and the precipitate, if any is recovered. The precipitate
represents asphaltenes insoluble in a particular sample tube. The
asphaltenes are subsequently washed in a normal paraffin,
preferably n-heptane or n-pentane. The recovered insolubles are
then weighed in preferably wt. % and plotted against the weight %
of n-heptane or n-pentane of the solution of the particular sample
tube.
The critical solvent power is calculated at the point of the
resulting plot where asphaltenes begin to precipitate. This is done
by determining the solvent power of the solution of the sample tube
where asphaltene precipitation began. The solvent power of the
solution is calculated as indicated in the solvent power
calculation procedure previously described. The difference in the
distillation curve will be in the amount of heptane recovered at
98.5.degree. C., the boiling point of heptane. The gravity of the
crude oil will also become less with the addition of heptane.
In addition to determining the critical solvent power of a crude
oil, the resulting plot results in a curve that describes the
asphaltene equilibrium between the precipitated and soluble states
of asphaltenes below the critical solvent power of the tested crude
oil. This curve is advantageous because it is useful in predicting
the total amount of asphaltenes in a crude oil and the amount of
asphaltene precipitation at various solvent powers below the crude
oil's critical solvent power.
Blending Two or More Crude Oils
If two or more crude oils are blended together, the blend solvent
power varies between the solvent powers of each crude oil.
Determining the solvent power for a two crude oil blend is
relatively simple since it can be calculated analytically. However,
as each additional crude oil is added to the blend, the degrees of
freedom increase such that the number of potential blends goes up
exponentially. For example, for five crude oils blended in 10%
increments, the number of blends to be evaluated for compatibility
is in the thousands. Consequently, it becomes increasingly
difficult to analytically compute the solvent power and
compatibility of the crude oil blend as the number of crude oils in
the blend increases. For this reason, a Monte Carlo simulation is
preferably used to select a representative number of different
blends to calculate the solvent power at each blend ratio and
compare to the critical solvent power of each crude oil, thereby
creating enough representative data points to accurately model the
blending compatibility of two or more crude oils.
The Monte Carlo simulation in its basic terms simply accounts for
the probabilities of each potential outcome for a potential
variable and uses a random number generator to assign a value to
each variable. As used in the subject invention, the Monte Carlo
simulation varies the fraction of each crude oil in a crude oil
blend preferably to a weight fraction probability distribution
function that the user provides. In a preferred embodiment, the
Monte Carlo simulation technique chooses random crude oil blend
ratios of selected crude oils. The weight fraction of asphaltenes,
if any, precipitated in the random crude oil blends is then
calculated at each of the randomly selected blend ratios.
When using the Monte Carlo technique, it is preferred to have a
stipulation that the error in the crude oil blend solvent power
calculation is not greater than a specified error. It is preferable
that the error in the crude oil blend solvent power calculation is
not greater than 0.5 SP (E=0.5). The number of iterations required
is preferably on the order of
##EQU00004## where r is the smoothness of the asphaltene solubility
curve and n is the number of crude oils in the blend. It is
preferred that r=0.3. Thus, for 2 crude oils in the blend, 100
random points are generated. For 3 crude oils in the blend, 1000
random points are generated.
It is assumed that the solvent power of the crude oil blends
linearly by weight. Saying this, the solvent power of the crude oil
blend is equal to the sum of the product of the weight fraction of
the crude oil in the blend to the solvent power of the crude oil,
which is given by:
.times..times. ##EQU00005## wherein SP.sub.blend is the solvent
power of the blend; X.sub.i is the weight fraction of crude i in
the blend; SP.sub.i is the solvent power of crude i; and n is the
number of crude oil in the blend.
To prevent incompatibility, the blend solvent power should be
greater than the critical solvent power of the crude oil having the
highest critical solvent power in the blend. It is preferable that
the blend ratio of the crude oils is at least about 15 vol. percent
greater than the blend ratio at the critical solvent power of the
crude oil having the highest critical solvent power in the blend.
It is even more preferable that the blend ratio of the crude oils
is at least about 10 vol. percent greater than the blend ratio at
the critical solvent power of the crude oil having the highest
critical solvent power in the blend. However, it is even most
preferable that the blend ratio of the crude oils is at least about
5 vol. percent greater than the blend ratio at the critical solvent
power of the crude oil having the highest critical solvent power in
the blend. Alternatively, it is preferable that the solvent power
of the crude oil blend is at least 15 percent greater than the
critical solvent power of the crude oil having the highest critical
solvent power in the crude oil blend. It is even more preferable
that the solvent power of the crude oil blend is at least 10
percent greater than the critical solvent power of the crude oil
having the highest critical solvent power in the crude oil blend.
However, it is even most preferable that the solvent power of the
crude oil blend is at least 5 percent greater than the critical
solvent power of the crude oil having the highest critical solvent
power in the crude oil blend.
Although the present invention has been described with
particularity and detail, the following example provides further
illustration of the invention and is understood not to limit the
scope of the invention.
EXAMPLE #1
Example 1, which is graphically depicted in FIG. 1, represents a
predictive model in accordance with the subject invention wherein
crude oil X, crude oil Y and crude oil Z are blended in a
three-component blend. As depicted in FIG. 1, the model ranges in %
vol. where the separate crude oils are compatible and incompatible
for blending. The X-axis represents % vol. of crude oil X and the
Y-axis represents % vol. of crude oil Y. The balance at any point
is the % vol. of crude oil Z. Crude oil X has a solvent power of
40.0 and critical solvent power of 27.2. Crude oil Y has a solvent
power of 37.3 and a critical solvent power of 30.1. Crude oil Z has
a solvent power of 22.2 and a critical solvent power of 16.6. In
addition to predicting the incompatibility of crude oil blends, the
"Incompatible Blend Range" range also illustrates the amount of
aphaltenes in % wt. expected to precipitate out of the crude oil
blend at that blending range.
EXAMPLE #2
Example 2 is a predictive model of process unit fouling (asphaltene
precipitation) resulting from the blending of various crude oils at
a refinery over a period of time. The model is graphically depicted
in FIG. 2 and numerically depicted in the Table. FIG. 2 depicts the
solvent power of the various blends in comparison with the critical
solvent power of the crude oil having the highest critical solvent
power in each blend. The solvent powers of each crude oil and each
crude oil blend were calculated as described herein. The critical
solvent powers of each crude oil were calculated as described
herein. The Table numerically illustrates FIG. 2 at selected
representative time periods. The Table also shows the solvent
powers of each crude oil in the various blends and the weight %
fraction each crude oil contributes to the various blends. The data
from Example 2 predicts that where the blend solvent power is less
than a critical solvent power of 26.9 significant fouling occurs in
refinery process units.
TABLE-US-00001 TABLE Period 1 Period 13 Period 23 Period 31 Crude
Wt. % Crude Wt. Crude Wt. Crude Wt. Oil SP Fract. Oil SP Fract. Oil
SP Fract. Oil SP Fract. A1 29.7 3.7 B1 31.0 14.8 C1 27.8 29.1 D1
27.8 11.6 A2 21.0 3.9 B2 22.1 11.5 C2 22.1 9.4 D2 22.1 16.2 A3 32.4
26.6 B3 32.4 9.0 C3 32.4 5.5 D3 32.4 2.6 A4 28.8 6.8 B4 28.8 3.0 C4
29.9 4.4 D4 26.8 13.0 A5 26.4 2.0 B5 29.9 23.0 C5 39.4 3.5 D5 16.4
6.5 A6 39.4 24.1 B6 26.4 2.0 C6 28.6 16.4 D6 19.7 15.5 A7 28.6 8.8
B7 39.4 16.0 C7 19.7 11.0 D7 26.1 12.7 A8 19.7 13.5 B8 28.6 12.0 C8
26.1 5.3 D8 22.2 7.6 A9 35.0 4.1 B9 19.7 2.7 C9 22.2 7.4 D9 23.3
14.3 A10 22.2 2.9 B10 26.1 3.1 C10 23.3 8.0 A11 23.3 3.6 B11 23.2
2.9 Blend SP: 30.6 Blend SP: 30.3 Blend SP: 26.4 Blend SP: 24.4
Crit. SP: 26.9 Crit. SP: 26.9 Crit. SP: 26.9 Crit. SP: 26.9
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